Penguins are undeniably adorable. What other animal waddles around in a little tuxedo? But don’t let that cute exterior fool you: on a 1910–1913 Antarctic expedition, surgeon and zoologist George Levick bore witness to some surprising sexual behaviors of Adélie penguins, including coerced sex and necrophilia. In fact, the paper he wrote on the penguins’ sexual habits was considered too explicit to be published during the Edwardian era, and has only recently been rediscovered after spending almost a century hidden away in the Natural History Museum at Tring.

Levick travelled to Antarctica with Captain Robert Scott’s 1910 Terra Nova expedition, where he spent 12 weeks in the world’s largest Adélie penguin colony at Cape Adare, observing the birds, taking photographs, and even collecting nine penguin skins. After his return, Levick used his daily zoological notes as source material for two published penguin studies, one for the general public and a more scientific one to be included in the expedition’s official report. Intriguingly, this second account includes vague references to “’hooligan’ cocks” preying on chicks. Levick merely writes, “The crimes which they commit are such as to find no place in this book, but it is interesting indeed to note that, when nature intends them to find employment, these birds, like men, degenerate in idleness.”

Now, modern-day researchers have discovered that Levick did in fact describe the hooligans’ crimes in the paper, “The sexual habits of the Adélie penguin.” This paper was expunged from his official account, probably because it was too disturbing for Edwardian mores. Levick himself covered some explicit passages of his personal notes with coded versions, rewritten in the Greek alphabet and pasted over the original entries. Although the paper was withheld from the official record, researchers at the Natural History Museum did preserve it in pamphlet form, printing 100 copies labeled, “Not for Publication.” But most of the originals have been lost or destroyed, and no later works on Adélie penguins cited this paper until recently, when researchers in the Bird Group at the National History Museum at Tring discovered one of the original pamphlets in their reprints section.

Coded section of Levick’s personal notes written in Greek alphabet

The text has been republished to reveal Levick’s detailed observations of the Adélie penguins’ sexual habits, which included auto-erotic behavior, homosexual interactions, coerced sex (including with chicks and injured birds), and necrophilia:

Strewn about all Antarctic rookeries are the dead bodies of many hundreds of penguins, from the adult to the newly-hatched chick, which have succumbed for various reasons during previous years. Owing to the low temperature prevailing, these bodies are preserved in good condition for a long time…When the season was already a month advanced, I saw a cock engaged in the sexual act upon the dead body of a white-throated Adélie of the previous year. This took somewhat over a minute, the position taken up by the cock differing in no way from that of normal copulation, and the whole act was gone through, down to the final depression of the cloaca and emission of semen…Later on, this sight was by no means uncommon.

Although he adopted an objective tone in his paper, Levick’s personal notes evince disgust. “There seems to be no crime too low for these Penguins,” Levick wrote, and this attitude perhaps explains why he made no attempt to interpret the penguins’ sexual behavior. Modern zoologists, however, have investigated why males would copulate when there was obviously no chance of reproduction. They suggest that the male urge to mate could be triggered when another bird’s position mimics that of a receptive female, a submissive pose with half-lidded eyes. In fact, researchers discovered that males would get down with just about any bird that assumed this mating position, whether it was an eligible female, a male, a chick, or even a rock attached to a frozen penguin head.

“why males would copulate when there was obviously no chance of reproduction.”

This sounds like a very silly question and is the same logic that would deduce that people eat fruit for the vitamins. That is the evolutionary advantage, but the mechanism has little to do vitamins (which are pretty tasteless to us) and has everything to do with a natural co-occurring entity to vitamins: sugar.